The present invention relates to a portable data collection device including an imaging-based dataform reader and, more particularly, to a portable data collection device including an imaging based dataform reader utilizing multiple target area illumination sources for independent reading of superimposed dataforms.
Portable data collection devices are widely used in manufacturing, service and package delivery industries to perform a variety of on-site data collection activities. Such portable data collection devices often include integrated bar code dataform readers adapted to read bar code dataforms affixed to products, product packaging and/or containers in warehouses, retail stores, shipping terminals, etc. for inventory control, tracking, production control and expediting, quality assurance and other purposes. Various bar code dataform readers have been proposed for portable data collection devices including laser scanners and one dimensional (1D) charge coupled device (CCD) imaging assemblies, both of which are capable of reading 1D bar code dataforms, that is, bar codes consisting of a single row of contrasting black bars and white spaces of varying widths. Both laser scanners and CCD imaging assemblies are also capable of reading a xe2x80x9cstackedxe2x80x9d two dimensional (2D) bar code dataforms, such as PDF417, which is comprised of a plurality of adjacent rows of bar code data. The stacked 2D bar code PDF417 includes row indicator patterns utilized by the dataform reader for vertical synchronization to permit reading successive rows of bar code data.
A two dimensional (2D) imaging based dataform reader has been proposed in U.S. Pat. No. 5,702,059, issued Dec. 30, 1997 and entitled xe2x80x9cExtended Working Range Dataform Reader Including Fuzzy Logic Image Control Circuitry.xe2x80x9d The 2D dataform reader disclosed in U.S. Pat. No. 5,702,059, which is assigned to the assignee of the present application, includes an imaging assembly having a two dimensional array of photosensors adapted to read 2D bar code dataforms (e.g., PDF417, SuperCode, etc.) with vertical synchronization row indicator patterns as well as matrix dataforms (e.g., MaxiCode, DataMatrix, etc.) which do not include vertical synchronization patterns. The individual photosensors correspond to image picture elements or pixels of the resulting image generated with the photosensors are read out after an exposure period or periods. The 2D dataform reader disclosed in U.S. Pat. No. 5,702,059 utilizes an open loop feedback control system including fuzzy logic circuitry to determine proper exposure time and gain parameters for a camera assembly. U.S. Pat. No. 5,702,059 is incorporated in its entirety herein by reference.
Two dimensional and matrix dataforms have a greater density of encoded data per unit area than 1D dataforms. However, even with 2D and matrix dataforms, there are limitations on the amount of data that can be encoded in a dataform applied to or imprinted on an item. First, there are limitations on the area of a product or a product""s packaging where a label imprinted with a dataform may be affixed or where a dataform may be directly imprinted. For certain items, any portion of the item may be acceptable for application of a dataform, thus, the acceptable area for dataform application is limited to the size of the item. However, for other items, the acceptable area for application of a dataform may be limited to a certain region having a generally flat surface suitable for label application or imprinting of a dataform. Second, a dataform reader is limited by a minimum cell size required by the reader. The minimum cell size of a dataform reader is the required size of the smallest individually readable portions of a dataform to be read by the dataform reader. If the minimum cell size of a dataform is less than the minimum cell size capable of being read by the dataform reader, successful decoding of the dataform is not possible.
In an imaging based dataform reader, the minimum cell size capable of being read is a function of a number of factors including the optic assembly and the illumination assembly of the reader. Generally, the smaller the minimum cell size required to be read by a dataform reader, the better the quality of the optics of the optic assembly will be need to properly focus a non-distorted image of the target area of the reader onto the photosensor array. Consequently, the smaller the minimum cell size that is required to be read, generally, the more expensive the optic assembly will be. Similarly, the smaller the minimum cell size that is required to be read, the more powerful and more focused the illumination assembly must be to provide an adequate intensity of illumination across the entirety of the target area of the reader. Again, the smaller the minimum cell size that is required to be read, generally, the more expensive the illumination assembly will be.
What is need is a method of generating a dataform having a high density of encoded data per unit area of the dataform but also having an acceptably large minimum cell size so that the need for an expensive optic assembly and illumination assembly to read target dataforms is ameliorated. What is further needed is a dataform reader capable of reading such a dataform without undue expense or the necessity of radically changing the imaging assembly from what is known in the art.
In accordance with this invention, a portable data collection device is provided with a two dimensional imaging assembly including a modular board camera providing for independent reading, that is, imaging and decoding, of superimposed dataforms. The dataform reader is provided with a targeting and illumination assembly comprising two illumination or radiation sources, each illumination source providing illumination in a different range of the electromagnetic spectrum. In a first preferred embodiment, the first illumination source provides illumination in the visible range, e.g., radiation having a wavelength range centered at about 6600 Angstrom or 660 nanometers (nm.) corresponding to the visible spectrum of light. The second illumination source provides illumination in the ultraviolet range of the electromagnetic spectrum, e.g., radiation having a wavelength range centered within the ultraviolet range which extends between about 200 Angstrom or 20 nm. to 3800 Angstrom or 380 nm.
The superimposed dataforms are printed on a substrate in a dataform area. The dataform area may be a label which is affixed to a product or a product""s packaging. In such a case, the dataform area substrate on which the superimposed dataforms are printed would be the label material. In other cases the superimposed dataforms may be imprinted directly on an area of the product or the product""s packaging. In these cases, the dataform area substrate would be the portion of the product or product packaging where the dataforms are printed. In accord with the present invention, two superimposed dataforms will be printed on a substrate in the dataform area. A first dataform will be printed on the substrate in the dataform area using a first pigment or ink for the printed cell portions of the first dataform and a second dataform will be printed on substrate in the dataform area using a second pigment or ink for the printed cell portions of the second dataform.
The ink used for the printed cell portions of the first dataform is a visible, non-carbon ink, that is, ink that absorbs light in the visible spectrum and does not absorb ultraviolet light. The ink used for the printed cell portions of the second dataform is an ultraviolet active ink, that is, ink that fluoresces upon being illuminated by ultraviolet light. When ultraviolet active ink fluoresces, it emits lights in the visible spectrum.
The imaging assembly of the present invention includes a modular board camera assembly having a two dimensional (2D) photosensor array, an optic assembly for focusing an image of the target area onto the photosensor array and the illumination assembly. In addition to providing multiple illumination sources to successively illuminate the target area, the targeting and illumination assembly also includes a targeting assembly to provide targeting illumination for focusing visible targeting illumination on the target area to aid a user in aiming the device.
In the preferred embodiment, the modular board camera assembly includes circuitry generating an analog composite video signal. The 2D photosensor array is a charge coupled device (CCD) comprised of a two dimensional matrix of photosensors. The composite analog video signal generated by the modular board camera assembly represents successive image frames of the imaging assembly target area. The composite video signal is converted by signal processing circuitry to a stream of eight bit digital gray scale values.
Upon instituting a dataform reading session, the targeting illumination assembly and the first visible illumination source are alternately energized to enable the operator to aim the device and simultaneously capture image frames of the target area wherein the target area is uniformly illuminated and does not include xe2x80x9chot spotsxe2x80x9d of illumination in the target area caused by the narrowly focused targeting illumination. Reflected illumination from the dataform corresponding to the pattern of the first dataform is focused onto the photosensor array. To avoid image distortion, the targeting illumination assembly is turned off so that image frames without reflected targeting illumination are generated. Decoding will be attempted on such a non-distorted image frame.
A portion of the set of gray scale values corresponding to the first captured image frame is converted by binarization and zoning circuitry into a set of binary (0,1) values in accord with a binarization algorithm. Working from a center of the image area outwardly, the circuitry identifies the binary values corresponding to the first dataform. The binary values corresponding to the imaged visible light dataform are operated on by cell extraction circuitry. The cell extraction circuitry generates cell extraction values which correspond to an image of the first dataform area. Decoding circuitry then operates on the cell extraction values to decode the first dataform.
Upon successful imaging and decoding of a captured image frame having an image of the first dataform, the first illumination source is deenergized and the second ultraviolet illumination source is energized. As with the first illumination source, the second ultraviolet illumination source and the targeting illumination assembly are alternately energized and to enable the operator to aim the reader and simultaneously capture image frames of the target area wherein the target area is uniformly illuminated and does not include xe2x80x9chot spotsxe2x80x9d of illumination in the target area caused by the narrowly focused targeting illumination. The ultraviolet light causes the ultraviolet active ink portions of the dataform to fluoresce and emit visible illumination. This illumination pattern resulting from the fluorescence corresponds to a xe2x80x9cnegativexe2x80x9d of the pattern of the second dataform. The illumination pattern is focused onto the photosensor array. Once again, to avoid image distortion, the targeting illumination assembly is turned off so that image frames without reflected targeting illumination are generated and decoding will be attempted on such a non-distorted image frame.
As before, the binarization and zoning circuitry convert a portion of the set of gray scale values corresponding to the second captured image frame into a set of binary (0,1) values in accord with the binarization algorithm. Working from a center of the image area outwardly, the circuitry identifies the binary values corresponding to the imaged UV light dataform. The binary values corresponding to the UV light dataform are operated on by the cell extraction and the decoding circuitry, as set forth above, to decode the UV light dataform. Upon successful imaging and decoding of a captured image frame having an image of the second dataform, the second illumination source is deenergized.